Method of manufacture for cathode-ray tubes for color television receivers

ABSTRACT

-A method of manufacture for cathode-ray tubes for -color television receivers of the type in which a grid consisting -of parallel metal wires is disposed in the tube facing the -front wall on which the television image is formed. The wires -of the grid are of a non-magnetic alloy with a high cobalt content, -as a rule more than 20 percent by weight, the composition further being such that in the course of heat treatment for joining the front portion of the tube with the conical portion by means of -a sealing compound, oxides favorable to the airtight connection between the alloy and the sealing compound appear at the surface -of the wires which renders unnecessary a second step of heat treatment for forming a sealing fillet at the outer ends of the wires.

United States Patent 1191 Lebel METHOD OF MANUFACTURE FOR CATI'IODE-RAYTUBES FOR COLOR TELEVISION RECEIVERS [75] Inventor: Pierre Lebel,Kremlin-Bicetre,

France [73] Assignee: France-Couleur, Paris, France [22] Filed: May 10,1972 [21] Appl. No.: 255,883

Related US. Application Data [62] Division of Ser. No. 35,831, May 8,1970,

abandoned.

[ 30} Foreign A p 1159111611 Pridrit fiat C Ma 20, 1969 France 69.16273[52] US. CI...IIIQII'IYLIIZI 35759,?5/57529: F/Zi,

161/195 [51] Int. Cl. C03c 27/02 [58] Field of Search 65/59, 43, 58;161/196; 29/472.9; 313/83 [56] References Cited UNITED STATES PATENTS2,043,307 6/1936 Scott 65/59 X 2,065,404 12/1936 Scott 16l/l96 2,147,4182/1939 Bahls 65/59 X 3,284,174 10/1966 Zlmmer 29/472 9 3,350,180 10/1967Croll; 161/196 X 3,467,509 9/1969 Foster et al 65/59 X 3,489,966 1/1970Bradu et al. 1 313/83 3,719,848 3/1973 Bradu 65/59 X [451 Sept. 24, 1974OTHER PUBLICATIONS Alloy Digest; Engineering Alloys Digest Inc. UpperMontclair, N.J.; August 1953; Filling Code: Co-4 (Cobalt Alloy) Elgiloy.Alloy Digest; Eng. Alloys Dig. Inc.; March 1956; Filing Code: Co-9(Cobalt Alloy) Cobenium.

Primary Examiner-S. Leon Bashore Assistant Examinerl(enneth M. SchorAttorney, Agent, or Firm-Charles E. Temko [5 7] ABSTRACT A method ofmanufacture for cathode-ray tubes for color television receivers of thetype in which a grid consistingof parallel metal wires is disposed inthe tube facing the front wall on which the television image is formed.The wires of the grid are of a nonmagnetic alloy with a high cobaltcontent, as a rule more than 20 percent by weight, the composition fur-4 Claims, 1 Drawing Figure METHOD OF MANUFACTURE FOR CATHODE-RAY TUBESFOR COLOR TELEVISION RECEIVERS This application is a division ofapplication Ser. No. 35,831, filed May 8, 1970 and now abandoned.

FIELD OF THE INVENTION The invention concerns the manufacture of picturetubes for color television receivers, particularly such tubes in which agrid comprising parallel metal wires is disposed in the tube facing thefront wall or screen on which is formed the image.

More particularly, the invention concerns the manufacture of tubesaccording to which each wire of the grid is held by the joining of thefront portion of the tube, or forward face comprising the screen, to themiddle-rear or conical portion of the tube.

PRIOR ART In the manufacture of color picture tubes, the front portionis joined to the middle-rear portion by means of a glass-base cement inwhich the ends of the wires, previously positioned between the twoportions of the tube, are embedded which thus simultaneously assures thesecuring of both the wires and the portions of the tube.

In the manufacture of such tubes at present, it has been found that thejoint thus obtained is not airtight and a second manufacturing step isnecessary according to which the joint between the two portions isprotected by additional filler material which is usually also cementsuch as that which is interposed between the edges of the two portionsof the tube and forms a outer fillet which straddles the joint.

The second step of manufacture is indispensable for assuring theairtightness; further, this step significantly increases the cost of thetube and causes additional mechanical stresses in the tube owing to theheat treatment of the second step and therefore increases the risk ofrupture or cracking the tube which may also lead to the tube beingdiscarded.

SUMMARY OF THE INVENTION My invention consists in a method for use inthe manufacture of color picture tubes with grids for joining the frontportion of the tube to the middle-rear portion by heat treatment andwith the aid of a sealing composition wherein the grid comprises wiresformed of a nonmagnetic alloy having a high cobalt content, and thecomposition of the alloy being such that during the course of the heattreatment oxides favorable to the formation of an airtight alloy-sealingcomposition joint are produced on the surface of the wires which renderunnecessary a second heat treatment step for forming an airtight filletabout the outer ends of the wires.

It is an object of my invention to provide a method of manufacturingsuch tubes which enables a reduction in the cost of such tubes and animprovement in the operation thereof.

Metal alloys which can be bonded to glass by heating are known and theappearance of metal oxides during the course of heat treatment which isfavored by the high content of cobalt in the alloy has been reported. Ithas not been possible however to form the wires of the grid of a colortelevision picture tube of such an alloy since such alloys are magneticand would affect the paths of the electron beams.

Other alloys having a high cobalt content are also known, but suchalloys have a coefficient of expansion very much different than that ofglass, so that until now it has not been proposed to use them in formingmetalglass joints.

It has now been found in an unexpected manner that certain non-magneticalloys having a high cobalt content can be used for the wires of a colortelevision picture tube grid and that the forming of a joint between theforward portion and the middle-rear portion of the tube according to theusual method with the interposition of the wires there between enablesthe formation of an airtight joint along the wires which rendersunnecessary the second step in the manufacture, i.e., forming a filletwhich until now has been unavoidable.

It is thought that this result arises from the small sections of alloyformed as the fine wires of the grid of a picture television tube.

The invention contemplates to make the wires constituting the grid of analloy having a high cobalt content, such as used in the manufacture ofcertain watch springs, which display excellent mechanical properties.

Such alloys generally correspond to the following formula:

carbon approx. 0.1% silicon approx. 0.3% manganese approx. 1.5% nickell0 30% chromium l0 30% molybdenum or tungsten 2 15% cobalt 25 45% ironapprox. 16%

Other features and advantages of the invention will become apparent fromthe description which follows.

BRIEF DESCRIPTION OF THE DRAWING The sole accompanying FIGURE shows asection of a color television picture tube in the vicinity of the zoneconnecting the forward portion to the conical portion for explaining themethod according to my invention.

DESCRIPTION OF A PREFERRED EMBODIMENT The forward portion 12 of a colortelevision picture tube formed of customary mild glass comprises ascreen 13 and a flanged portion 11 having an edge 10. Along the edge 13is spread a layer 14 of a sealing or bonding mixture of the type whichis currently used in such a method and which is a suspension of powderedglass in a base having a low viscosity (nitro-cellulose in amyleacetate) as is known in the art under the name Pyroceram.

A network of parallel prestressed wires 16 having a diameter in theorder of 5/100 mm is interposed between the conical portion and theforward portion 12 and has the following composition by weight:

carbon 0.1% silicon 0.3% manganese 1.5% nickel 16% chromium 20%molybdenum 6% cobalt 40% iron 16.1%

This alloy, known under the name Phynox, is currently used in themanufacture of certain watch springs.

The combination is subjected to the usual heat treatment, i.e., startingfrom ambiant conditions, raising the temperature to 440C in one and onehalf hours, maintaining this temperature for one hour, then returningthe temperature to the ambiant temperature in approximately two hours.

At temperatures higher than 440C, the glass of the soldering material istransformed into a partial crystalline structure which results in abonding of devitrified glass.

During the lowering of the temperature, the wires are additionallytensioned owing to the coefficient of expansion of the alloy of whichthe wires are formed said coefficient being greater than that of theglass without however effecting the quality of the bonding apparentlybecause of the high modulus of elasticity of the alloy which is used.

It has been found that the joint thus effected is absolutely airtight,in particular, there is no leak along the lengths of any of the wires.

It thus becomes unnecessary to recover the joint on its exterior with afillet of the same material which is used as the sealing compound and tocarry out another heat treatment.

The risk of rupture or cracking of the tubes thus produced is much lessthan that of known types of tubes with grids.

The tubes resisted without difficulty variations in temperature in spiteof the fact that the coefficient of expansion of the alloy used is 135 Xquite larger than that of the sealing composition in which the wireswere embedded which is from 89 X 10 to 94 X 10 The high modulus ofelasticity of the alloy as well as the high yield point enables it towithstand higher tensions than the wires that are presently in use whosemodulus of elasticity and yield point are lower.

What I claim is:

l. in a method of manufacture by heat treatment of a color televisionpicture tube of the type including a front portion and a conicalmiddle-rear portion formed of mild glass and assembled by use of a glassbonding compound with a grid interposed between the portions. the stepsof forming the grid from wires of a substantially non-magnetic alloyhaving a cobalt content of at least 20 percent by weight to a diameterof approximately .05mm. and positioning said grid so that the ends ofthe wires extend outwardly of said bonding compound, whereby. owing tothe composition of the alloy, oxides are formed on the surface of thewires as a result of said heat treatment, which enables the formation ofan airtight bond between the wires and said bonding compound, whereinsaid wires are placed in tension.

2. A method in accordance with claim 1, wherein the alloy contains atleast 20 percent cobalt by weight. at least l0 percent chromium byweight, and at least 2 percent of a metal chosen from the groupconsisting of molybdenum and tungsten.

3. A method in accordance with claim 2, wherein the composition of thealloy corresponds to the following formula by weight:

Carbon Approx. 01% Silicon Approx. 0.3% Manganese Approx. 1.5% NickellO-307r Chromium 10-30% A metal chosen from the group 245% consisting ofmolybdenum and tungsten Cobalt 25-45% Iron Approx. 16%

4. A method according to claim 3, wherein the wires are formed of analloy having the following composition by weight:

Carbon Approx. .l% Silicon Approx. .39: Manganese Approx. l.5% Nickell67r Chromium 207: Molybdenum 6% Cobalt 40% Iron 16.1%

2. A method in accordance with claim 1, wherein the alloy contains atleast 20 percent cobalt by weight, at least 10 percent chromium byweight, and at least 2 percent of a metal chosen from the groupconsisting of molybdenum and tungsten.
 3. A method in accordance withclaim 2, wherein the composition of the alloy corresponds to thefollowing formula by weight:
 4. A method according to claim 3, whereinthe wires are formed of an alloy having the following composition byweight: